The resonator element can be for example a piezoelectric resonator, such as a quartz resonator to be connected to an oscillator circuit. Most quartz resonators of small dimensions, which are used for example in electronic or electromechanical watches, are quartz tuning fork resonators. These quartz resonators are usually enclosed in cases in vacuum, in the case of generating low frequency signals supplied by the oscillator circuit, or in an inert gas atmosphere.
Generally, such resonators are mounted in ceramic cases for example, which are relatively flat. These cases generally include a main part of parallelepipedic shape inside which a resonator is mounted, and a rectangular cover fixed onto the main part. If the resonator is enclosed in vacuum in the case, said resonator can be adjusted optically through the transparent cover.
In this connection, JP Utility Model No. 54-35870 can be cited, which discloses an electronic component with a resonator element, which is arranged in a first housing of a main part of a case. This first housing is hermetically sealed by a transparent cover fixed using a preform on an annular edge of the first housing of the main part. An integrated oscillator circuit is arranged in a second housing of the main part of the case, which is separated from the first housing by a base. The second housing is closed by an opaque cover fixed onto an annular edge of the second housing of the main part. The integrated circuit is electrically connected to the resonator element through the base of the main part of the case.
One drawback of such an electronic component disclosed in JP Utility Model No. 54-35870 is that, in the event of lateral shocks on each cover, cracks can occur in the cover or the material fixing the cover onto the main part, thus inducing a loss of sealing. These lateral shocks can occur during various manipulations, particularly during operations for assembling said electronic component in an electronic apparatus or on a printed circuit board. As the resonator element usually has to remain enclosed in vacuum in its case or in an inert gas atmosphere, the adjustment of the resonator element to generate signals of a determined frequency from the oscillator circuit may be impaired. The resonator can even stop oscillating. In order to minimise these problems, the corners and side faces of the covers have to be ground in accordance with special processes. Of course, this substantially increases the cost of such covers.
Another drawback of the electronic component of JP Utility Model No. 54-35870 is solely connected to the sealing method. Indeed, the technique commonly employed for sealing the case is to stack the various elements in a cavity of a metal plate, namely the preform on the main part of the case, and the cover on the preform. Thus, the three elements are accurately positioned. In order to do this, the mechanical tolerance of the cavity has to be very high so as to position the three elements properly.
It is thus a main object of the invention to overcome the drawbacks of the prior art by providing an electronic component having a resonator element hermetically enclosed in a case whose cover is protected from lateral shocks. Moreover, the manufacturing time and costs for such an electronic component with a protected case cover can be minimized.